Aluminum/lithium/x materials

ABSTRACT

Exposure to radiation is ordinarily countered by lead shields or lithium compounds with large nuclei and small electron clouds. Unfortunately lead is heavy and the effective lithium compounds are highly reactive and structurally unsuitable. 
     This invention takes thin sheets of aluminum-lithium alloy and rearranges the atoms into lithium-rich and aluminum-rich layers in alternate strata and laminates them into a sandwich structure with multiple lithium-rich layers and aluminum-rich layers. 
     Each individual sheet is heat treated as discussed in U.S. Pat. No. 6,069,197 and project NaAMTCO-330 ONR N00014-94-2-001 University of New Orleans/U.S. Navy by Alfred Daech. The individual sheets are heated under an argon or nitrogen blanket to cause the lithium in the alloy to concentrate at the surfaces. These sheets are then stacked to the desired final thickness. Lamination may be with or without adhesive. The final laminate is water washed to remove raw reactive lithium from the final handling exterior surfaces.

CROSS REFERENCED TO RELATED APPLICATIONS

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FEDERAL FUNDING

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BACKGROUND OF INVENTION

It is necessary to expend large amounts of energy to propel a space vehicle to escape the Earth's gravitational pulls. Once in space the propulsion required to send the vehicle further into space becomes considerably less while radiation increases in intensity. Dangerous radiation threatens the astronauts who are working on projects in orbit on the space station or other space vehicles and may damage or destroy the experiments being conducted. We deal with the issue of extra weight when heading into low Earth orbit and the degradation by radiation in this application namely by reducing the weight of the materials on the way to space and increasing space radiation protection and bacterial contamination resistance by using aluminum/lithium alloys.

Aluminum/Lithium/X Materials SUMMARY OF DISCLOSURE

This invention relates to improvements in material compositions utilized to provide protective layers on surfaces of vehicles sent to orbit and provide protection from radiation, corrosion, and bacteria thereafter.

In one application micro-fine flakes or continuous surfaces such as sheet and plate may be used to protect objects exposed to damp environments by killing surface bacteria. An example is vehicle interiors occupied by astronauts and certain sensitive equipment especially when prolonged exposure is encountered.

As the atmosphere is reduced the intensity of the radiation increases to a point where it can be lethal. Stopping the radiation with such dense material as lead is impractical due to the weight penalties. The aluminum/lithium alloy blocks radiation without taxing the payload with a heavy weight burden. Aluminum/lithium is light due to the low molecular weight, so that less effort is required to lift the metal to orbit.

A particular advantage of the alloy is that the system of aluminum and lithium is free of heavy metals. Heavy metals can have serious consequences in the environment. Elements such as lead, chromium, and cadmium may have grave impacts on health. The lighter elements are generally less offensive.

Not only is aluminum/lithium more ecologically acceptable, tests showed lithium is able to be concentrated by heat treatment to relocate lithium in the alloy to the surface of the metal as described in U.S. Pat. No. 6,069,197. Having the lithium on the surface is important because when it is normally dispersed randomly throughout the aluminum matrix it allows pathways for radiation penetration however as the lithium is concentrated on the surface it provides a close-knit barrier to radiation. It also provides a concentrated surface to fight bacteria.

Another advantage of the aluminum/lithium alloy is that it provides corrosion resistance for steel and aluminum substrates. These advantages are covered in U.S. Pat. No. 6,069,197 again by the same author of this invention.

The metallic alloy may be used in sheets, flakes, or powder form. The flake or powder is held in a suitable system such as epoxy resin. Lithium in a sheet or plate or powder can be concentrated on the surface of the alloy providing a shield against radiation. The lithium being of low molecular weight has a dense nucleus and a small electron orbital cloud. It is the nucleus which absorbs or reflects impinging radiation and the small electron cloud allows compactness.

The composition of the instant invention may also contain compatible filler to influence properties such as color, adhesion, wetting, ease of manufacture, stability, and other alloying advantages so long as these additives do not adversely affect the desired characteristics. Pure lithium without the alloying aluminum is much too reactive for practical use in most applications but the alloy is stable and more utile.

The aluminum/lithium also exhibits enhanced performance by the heat treatment described in U.S. Pat. No. 6,060,197 as well by the same author of this invention. Heating the aluminum/lithium to 350° Celsius for fifteen minutes produces a migration of the lithium to the surface of the alloy thereby improving the available lithium in the alloy at or near to the surface.

Having described the general details of the invention, the following alloy is presented as typical:

-   1% lithium, 92.2% aluminum, and 6.8% other elements.     This typical alloy combination was heat treated under an argon     blanket for 15 minutes at 350° Celsius and then rapidly cooled to     lock in the lithium at the surface. ESCA-AUGER confirm the lithium     was indeed on the surface. Although the alloy is effective without     the heat treatment, the performance is much enhanced by heating.     Heating for longer than 15 minutes or at higher temperatures than     350° Celsius begins to make the treatment less effective and at the     extremes of 400° to 500° Celsius the lithium is nearly depleted from     the alloy.

Thin sheets of the alloy may be laminated after heat treatment in order to make the material even more effective at filtering out the radiation. Sheets of pure lithium metal cannot be handled without considerable danger because of its inflammatory properties. The lithium in the alloy can migrate making the laminated product firmly bound and yet more easily handled. Laminated layers can more effectively combat radiation and thus save weight.

Other alloying metals with the aluminum which have been incorporated at 7% or less such as magnesium, copper, zinc, and the like do not greatly change the lithium function. Increasing the concentration of lithium at the surface of the alloy makes the surface more alkaline. At pH's above 10 or so these surfaces are toxic to bacteria. Bacteria can be the first step in a sequence of nutrients for progressively more dangerous contaminants. Work done at Louisiana State University by Dr. Ralph Portier, et al. in the “Materials Performance” publication dated October 2004 provides more details on this phenomenon.

The following are specific formulations made in accordance with the instant invention:

EXAMPLE I For Steel Substance

Component Parts by Weight Lithium Silicate 100 Aluminum/Lithium Powder 59.4 240 Mesh (92.2% Aluminum, 6.8% Magnesium, 1.0% Lithium) Mica (329 Mesh) 7.5 Lithium Molybdate 0.5 Sodium Borate Decahydrate 0.4 Total 167.8

EXAMPLE II For Aluminum Substrate

Component Parts by Weight Aluminum/Lithium Powder 64.5 240 Mesh Potassium Silicate 60.0 Solution Total 124.5

EXAMPLE III Sheet or Plate

Aluminum/Lithium alloy 2290 sheet was heated as described for 15 minutes under an Argon (or Nitrogen) blanket.

EXAMPLE IV Sheet or Plate

10 Sheets or plates of Aluminum/Lithium 1.0 mil. In thickness each heat treated to orient the Lithium and laminated front to back for radiation resistance.

The migration of the Lithium has been verified by ESCA-AUGER to show the Lithium concentration. 

1. An aluminum/lithium heat treated alloy formulation for protecting steel, aluminum, wood and the like from: radiation damage by concentrating the lithium in the alloy.
 2. An aluminum/lithium alloy which discourages the set down of bacteria on surfaces.
 3. An aluminum/lithium alloy in claim 2 with the surface of the alloy at pH10 or above and consequently repulsive to bacteria and some higher trophic organisms.
 4. An aluminum/lithium heat treated alloy with the lithium preferentially concentrated at the surface in order to provide increased absorbance to radiation and thus save weight.
 5. The material in claim 1 which is laminated in sheets so that multiples of oriented heat treated layers of 0.1 mils. to 10.0 mils. provide multiple radiation shields.
 6. The material in claim 1 where the lithium is 0.1 to 6.0 percent by weight of the aluminum/lithium alloy.
 7. The material in claim 1 where the alloy of aluminum/lithium has been heated to 300° C. to 350° C. under an inert gas atmosphere for 10 to 15 minutes thereby concentrating the lithium at the surface of the alloy.
 8. The material in claim 3 where the hygienic protection facilitates sanitary decontamination of surfaces. 